RE: [ASRG] 0 - General, Reliability of Transport

[Daniel Feenberg <feenberg at nber.org>]

On Wed, 26 May 2004, Chris wrote:

> 
> 
> >
> >   In my case, it's a 550 reject message *TO THE SENDING MTA, NOT AN
> > INNOCENT THIRD-PARTY WHOSE ADDRESS HAS BEEN FORGED IN ENVELOPE_SENDER*.
> >
> 
> Hence my enthusiasm for sender identification systems, such as spf/DK etc..
> 
> That way the actual sender gets the rejection notice, and can take measures.
> especially if it indicates their machine has been compromised.
> 
> only minimal if any good will come from bouncing it to the last known good
> MTA.
> 

Would you expand on this? I would think that if the message is legitimate,
the connecting MTA would be able to return to the actual sender an
indication that the message was not delivered if it got a 550 during the
transaction. Are there common circumstances under which it could not? Are
you thinking of a spammer forging an envelope from within the domain of
the connecting MTA? That would imply a spam friendly ISP, and would only
send spam to other users of that ISP. Even the laziest ISP would prevent
that, I should think.

Or does the problem occur when actual spam is rejected? Are you thinking
that the connecting MTA might generate a bounce message to a forged
address? I don't recall seeing much/any spam of that form in my mailbox. I
don't think those bounces contain the body of the message, so the spammer
doesn't have any incentive to take advantage of such behavior, and such an
MTA would look like any other spam source, and be blacklisted, but is
there any other reason such messages are so rare?

Daniel Feenberg





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